Doped Yb (3 +) Fiber Ultrashort Pulse Laser

The dissertation focuses on Yb3+-doped fiber laser. Both passively mode-locked Yb3+-deoped fiber ring laser and conventional Yb3+-deoped fiber ring laser were studied. The dissertation includes the detailed descriptions on the following subject:1.The study of the conventional Yb3+-deoped fiber laser.(1) The theoretical study of the Yb3+-deoped fiber laser includes:A. According to the rate equation, based on C. Barnard theory, expressions of the Yb3+-deoped fiber laser's threshold value, slope efficiency and output power were deduced. The relations between performance parameters and structure parameters were also studied.B. According to the theoretical analysis of pumping mode, we confirmed that two-end pumping can decrease the injecting power density, and gain distributing is more uniform in the fiber. We also confirmed that back-pumping can increase the output power of fiber laser and also can make the gain distributing uniform.(2) The experimental study of the conventional Yb3+-deoped fiber ring laser includes:A. Different length of Yb3+-deoped fiber was used to study the relations of laser's threshold, slope efficiency, output power to the doped fiber length.B. We also experimentally studied the relations of laser's threshold, slope efficiency, output power to pumping mode.C. We carried out experiment research of Yb3+-deoped fiber ring laser with different couple ratio and studied he relations of laser's threshold, slope efficiency, output power to couple ratio.D. Yb3+-deoped fiber ring laser working at 1053nm with narrow bandwidth was realized by using band-pass filter.2. The study of passively mode-locked Yb3+-deoped fiber laser.(1) The theoretical research of the passively mode-locked Yb3+-deoped fiber laser includes:A. Studied the parameters of laser's pulse width, chirp, bandwidth and stability by using different master equations which describes the characteristics of two kind of typical mode-locked lasers (mode-locked by fast saturable absorbers or commode-locked by fast and slow saturable absorbers). Analysis results show that positive dispersion increases the chip and pulse width of mode-locked pulses, and it is necessary to reduce incavity positive dispersion as much as possible to obtain short pulse width output.B. Parameters which influence on the self-starting and stability of the mode-locked Yb3+-deoped fiber ring laser were analyzed by using NLS equation, and numerical resultswere deduced. Analysis results show that mode-locked laser is easier self-started with higher third-order nonlinear gain coefficient and longer gain relaxation time. It also shows better filter effect, larger dispersion, larger saturable power of the gain medium, larger small signal gain and smaller incavity loss are propitious to laser's self-starting. Appropriate pump power and output couple ratio can increase the stability of the laser.(2) Experimental study of passively mode-locked Yb3+-deoped fiber laser.A. Using highly doped Yb3+ fiber for the first time in China, passively mode-locked by NPE, we generated pulses with bandwidth of 6nm, repetition rate of 20MHz. The center wavelength was 1045.58nm, and the maximum output power was 25mW.B. Based on the experiment, we propose alternative scheme to guide further fs Yb3+-deoped fiber laser research, which includes:a.We plan to shorten the cavity length to less than 5m, and then use fiber amplifiers to CPA amplify the chirped pulse output by the laser. The amplified pulse will be compressed by bulk grating pair.b. Redesign the laser, using and CFBG to compensate the incavity dispersion, or incorporating CFBG and polarization beam splitter to compensate the incavity dispersion, by which could realize the tuning of the output pulse width .